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Neuromuscular Physiology
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
Actin molecules exists in a globular form (G-actin), which is made of a single peptide chain and a filamentous form (F-actin) (Figure 1.11a). Actin filaments (F-actin) result from the polymerization of G-actin monomers. F-actin myofilaments consist of two G-actin polymers wrapped around each other, creating a double helix with a 360 Α period, and form the thin filaments of the sarcomere. Each actin myofilament contains about 350 G-actin molecules. In solution, actin and myosin bind, forming actinomyosin, strands of which will contract in the presence of ATP (127).
Smooth Muscle
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
Smooth muscles contain actin and myosin but are not striated. Actin filaments that form the contractile units are attached to dense bodies, which are dispersed inside the cell and held together by a scaffold of structural proteins. Myosin filaments are interspersed among the actin filaments. The cells have one nucleus, are about 4 μm in diameter and up to 400 μm long and are held in bundles by connective tissue. Troponin is absent and its regulatory role is taken over by calmodulin.
Genomics and Hearing Loss: Toward a New Standard of Care?
Published in Stavros Hatzopoulos, Andrea Ciorba, Mark Krumm, Advances in Audiology and Hearing Science, 2020
Myosins are actin-based molecular motors that regulate several processes, such as the rearrangement of the actin cytoskeleton, the regulation of tension of actin filaments and the transport of organelles. Several mutations affecting the myosins are well identified (MYO3A, MYO6, MYO7A, and MYO15A for example). Most of the mutations in MYO7A cause Usher syndrome type I, an autosomal recessive genetic disorder characterized by congenital, bilateral, profound sensorineural hearing loss, vestibular areflexia, and adolescent-onset retinitis pigmentosa. Usher syndrome represents about half of cases where both blindness and hearing impairments are present.
F11R/JAM-A: why do platelets express a molecule which is also present in tight junctions?
Published in Platelets, 2023
Piotr Kamola, Anna Babinska, Tomasz Przygodzki
F11R/JAM-A is a component of tight junctions. In these structures, extracellular parts of F11R/JAM-A molecules are assembled as cis-homodimers interacting via trans-homodimerization with cis-homodimers on adjacent cells.2 The intracellular part of the protein is associated with a complex of proteins which integrates tight junctions with the actin filaments. These trans-homophilic interactions are crucial for maintaining the integrity and regulation of permeability of an endothelial or epithelial layer. There are, however, discrepancies as to whether F11R/JAM-A plays a structural or regulatory role in these phenomena. A profound analysis of JAM-A’s role in the physiology of tight junctions and discussion regarding these discrepancies can be found in excellent reviews by Hartmann et al.42 and Steinbacher et al.21
Solanaceae glycoalkaloids: α-solanine and α-chaconine modify the cardioinhibitory activity of verapamil
Published in Pharmaceutical Biology, 2022
Szymon Chowański, Magdalena Winkiel, Monika Szymczak-Cendlak, Paweł Marciniak, Dominika Mańczak, Karolina Walkowiak-Nowicka, Marta Spochacz, Sabino A. Bufo, Laura Scrano, Zbigniew Adamski
Calcium ions are crucial for the contraction of all types of muscles. After influx into the cytoplasm, they interact with myofilaments and ultimately allow for interaction between myosin and actin filaments, and thus for muscle contraction. Since they are a trigger and an executor of muscle contractions, their concentration in the sarcoplasm must be strictly regulated. In striated muscles, cell membrane depolarization is a signal that initiates the cascade responsible for muscle contraction. Changes in the cell membrane potential activate and open the L-type calcium channels. Then, the local increase in Ca2+ concentration activates the ryanodine receptor, a sarcoplasmic calcium channel, which releases the next portion of calcium ions into the cytoplasm, which interacts with myofilaments.
Dual role of E-cadherin in cancer cells
Published in Tissue Barriers, 2022
Svetlana N. Rubtsova, Irina Y. Zhitnyak, Natalya A. Gloushankova
Actin filaments nucleate at AJs,27 but the mechanisms of actin filament polymerization at AJs are not well understood. It has been suggested that the Arp2/3 complex is involved in the nucleation of junctional actin filaments as it was shown that establishment of E-cadherin-based adhesion promotes recruitment of Arp2/3 to the AJs.28 Activators of the Arp2/3 complex, such as WAVE and N-WASP, have also been detected at epithelial AJs.22,29 Cortactin, which directly binds WAVE2 and Arp2/3 at ZA, may also regulate the junctional actin cytoskeleton.30 Formins promoting elongation of linear actin filaments may be involved in the assembly of actin filaments at AJs. It was demonstrated that RhoA effector Dia1 was essential for the formation and maintenance of linear AJs in MCF-7 cells.31 In MCF10A cells grown in Matrigel, the junctional actin assembly was mediated by Formin-like 2 downstream of Rac1.32